Molecular Mechanisms of Retina Pathology and Ways of its Correction

96 Pages·2020·3.129 MB·English

by  Svetlana Trofimova

Svetlana Trofimova
Molecular
Mechanisms
of Retina Pathology
and Ways of its
Correction
Molecular Mechanisms of Retina Pathology
and Ways of its Correction
Svetlana Trofimova
Molecular Mechanisms of
Retina Pathology and Ways
of its Correction
Svetlana Trofimova
St. Petersburg Institute of Bioregulation and Gerontology
Saint Petersburg, Russia
ISBN 978-3-030-50159-4 ISBN 978-3-030-50160-0 (eBook)
https://doi.org/10.1007/978-3-030-50160-0
© Springer Nature Switzerland AG 2020
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Contents
1 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Age-Related Characteristics of the Retina . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Molecular Mechanisms of Age-Related Macular
Degeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Molecular Mechanisms of Retinal Ischemia . . . . . . . . . . . . . 6
1.1.3 Molecular Mechanisms of Retinitis Pigmentosa . . . . . . . . . . 7
1.1.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 Current Trends in the Treatment of Retinal Diseases . . . . . . . . . . . . 9
1.3 Results of Modern Scientific Research in the Field of
Cell Replacement Therapy Using Neuronal Stem Cells . . . . . . . . . . 14
1.4 Biological Effects of Peptide Bioregulators . . . . . . . . . . . . . . . . . . . . 17
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2 Results of Experimental Studies of Short Peptides (Cytogens) in
Ophthalmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.1 Results of a Study of the Induction Effects of Short Peptides on
Pluripotent Embryonic Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.1.1 Methods of Morphological Assessment . . . . . . . . . . . . . . . . . 45
2.2 The Effect of Short Peptides on the Proliferative Activity
of Retinal Cells and Pigment Epithelium. . . . . . . . . . . . . . . . . . . . . . 50
2.2.1 Method of Preparation of Substrates for Cell Cultures . . . . . 50
2.2.2 Method of Obtaining Cell Cultures of the Retina
and Pigment Epithelium of Rats . . . . . . . . . . . . . . . . . . . . . . 51
2.2.3 Drug Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.2.4 Methods for Spectrophotometric Assessment
of the Number of Living Cells in Suspension . . . . . . . . . . . . 52
2.3 Effect of Short Peptides on Expression of Markers
of Differentiation of Retinal Neurons and Pigment Epithelium . . . . 54
2.4 Effect of Short Peptides on the Nature of the Course of Hereditary
Retinal Pigment Degeneration in Campbell Rats . . . . . . . . . . . . . . . 56
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
v
vi Contents
3 Results of the Clinical Study of Short Peptides (Cytogens) in
Ophthalmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.1 Evaluation of the Effectiveness of Short Peptides (Cytogens)
in Patients with Age-Related Macular Degeneration . . . . . . . . . . . . . 69
3.2 Evaluation of the Effectiveness of Short Peptides (Cytogens)
in Patients with Retinitis Pigmentosa . . . . . . . . . . . . . . . . . . . . . . . . 74
3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Chapter 1
Literature Review
Abstract The chapter describes age related structural features and functions of the
retina, as well as modern methods of treating degenerative diseases of the retina.
It is known that pathology of the retina (age-related macular degeneration, reti-
nitis pigmentosa) is a complex problem for clinical ophthalmology. Modern meth-
ods of treating retinal diseases (laser exposure, surgical treatment, drug administration
(such drugs as Lucentis, Macugen, Visudyne)) aim to only reduce the risk of new
complications in the eye. It must be emphasized that pathogenetic therapy of degen-
erative diseases of the retina is almost absent in international ophthalmic practice,
which leads to irreversible blindness in patients. Therefore, in order to search for
pathogenetic treatment, numerous studies are currently underway using the achieve-
ments of molecular biology.
This chapter reviews the results of various scientific studies in the field of cell
replacement therapy using neuronal stem cells in order to restore the functional
activity of retinal neurons.
In addition, the retinoprotective effect of peptide bioregulators is described and
the mechanisms of their activity are defined. For example, research results are pre-
sented showing that peptides are able to stimulate the expression of cell differentia-
tion markers by binding to promoter regions of genes, which is necessary for the
development, interaction and functioning of cells.
1.1 Age-Related Characteristics of the Retina
Age-related changes in eye tissues are subject to the general laws of body aging, but
at the same time, they have their own characteristics, due to the structural and func-
tional specifics of the visual analyzer and the presence of an autoregulation mecha-
nism in its blood supply system (Arking 1998; Wong et al. 2014).
Age-related retinal pathology is largely determined by the features of its histo-
logical structure. To date, physiological and biochemical mechanisms of photo-
activation which ensure perception and amplification of the primary light signal are
known, as well as morphological features of the structure of its layers. The retina is
a thin layer of tissue that lines the back of the eye on the inside. Histologically, the
retina consists of ten layers of nerve cells that are morphologically and functionally
interconnected. It is composed of six types of neurons and one type of glial cells
© Springer Nature Switzerland AG 2020 1
S. Trofimova, Molecular Mechanisms of Retina Pathology and Ways of its
Correction, https://doi.org/10.1007/978-3-030-50160-0_1
2 1 Literature Review
which form a highly organized layered structure. The main layer of the retina is a
thin layer of photosensitive cells, photoreceptors (rods and cones). The main func-
tion of the retina is to convert the light signal detected by photoreceptors into an
electrical impulse transmitted to the brain. Age-related dysfunction of retinal cells
leads to disruption of normal nerve signal formation and, as a result, to visual
impairment (Wiedemann and Kohen 1997; Singer 2014).
Older people experience a decrease in visual acuity and colour perception, asso-
ciated in most cases with the death of retinal neurons. Of all retinal cells, photore-
ceptors are most susceptible to aging. One of the reasons for this is oxidative stress
(imbalance between the systems of generation and detoxification of reactive oxygen
species) due to exposure to light. Ultraviolet radiation induces the formation of free
radicals, which cause oxidative damage to the walls of the membranes of the retinal
cells and trigger lipid peroxidation (Shaw et al. 2016). All this launches involutional
processes in the retina of the eye and the occurrence of degenerative retinal changes.
Additionally, age causes a physiological decrease in the number of neuronal cells in
the retina. So, according to A. Neufeld (2001), this process is ongoing. Over the
course of several years, he observed several species of test animals, whilst evaluat-
ing the age-related loss of ganglion cells. The research results showed that every
month there was a decrease in the number of ganglion cells in the retina in all ani-
mals. Moreover, in the group of mice this indicator amounted to 2.4% of the monthly
loss of ganglion cells, while in rats this indicator was lower and amounted to 1.5%
of the monthly loss. However, by the end of life, this indicator reached a single
value: 35% in both groups of animals. In addition, artificially induced retinal isch-
emia (within 75 min) further exacerbated the existing picture. There was a 20%
decrease in the number of ganglion cells in the group of young animals and a 35%
decrease in the group of old rats. Thus, the retinas of old animals turned out to be
more sensitive to damaging agents than young ones. According to the author, a simi-
lar decrease in the number of ganglion cells with age occurs in the retina of pri-
mates, including humans. Therefore, Neufeld A. naturally concludes that age-related
degenerative changes in the retina occur due to a significant decrease in the number
of ganglionic retinal cells, especially under the influence of unfavourable factors
(Neufeld 2001). This can explain the fact that the number of rods and cones in
people aged 60 and above is twice as low as that in 20-year-olds. Similarly, there is
a decrease in the number of bipolar and ganglion cells in people aged from 35 to 60.
With aging, degenerative changes in the optic nerve fibres are also observed.
They are replaced by connective tissue, and the inner border membrane thickens.
Ganglion and bipolar cells accumulate lipids, while astrocytes actively express glial
fibrillar acidic protein (Zueva 2010). According to some authors, dystrophic pro-
cesses are based on the metabolic disorders of specific proteins in the pigment epi-
thelium, as well as other layers of the retina (Curcio 2018; Friedman et al. 1998).
Involutional changes in the layer of retinal pigment epithelium are expressed in a
significant reduction in the number of nuclei, the sparseness of nuclear spaces, and
the flattening and shortening of pigment cells. With age, morphological changes in
the Bruch’s membrane occur: it thickens, appears to be curved, and sudanophilic
masses and lipids start depositing. Accumulations of amyloid fibrils are found in the
1.1 Age-Related Characteristics of the Retina 3
inner collagen layer of the membrane. It has been suggested that during involutional
degeneration of the retinal pigment epithelium in the cytoplasm of these cells, non-
phagolized neuroepithelial discs accumulate, from which fibrils of the pathological
amyloid protein are subsequently formed (Ermilov and Vodovozov 1995; Ermilov
and Trofimenko 1998). In a test on C5BL/6 mice (2-, 9-, and 16-month old), a cor-
relation between the degree of subretinal deposits and age was revealed (the authors
evaluated the number of subretinal druses using points as an assessment unit). In
16-month-old mice this indicator was 2.5 times higher than that of young animals.
In addition, according to the authors, a diet with a high content of high-density lip-
ids, as well as ovariectomy, which leads to hormonal imbalance, can provoke
destructive changes in the retina. However, lipid metabolism disturbance occurs
mainly in organisms with a genetic predisposition to this, which is confirmed by the
results of the experimental studies of T. Ikeda. The authors indicate that presence of
a paraoxanase polymorphism gene leads to disruption of lipid metabolism and, as a
consequence, the appearance of age-related macular degeneration (Ikeda et al. 2001).
With the degeneration of photoreceptors, changes in the nerve layers of the retina
are observed (Marc et al. 2003). Restructuring of the nerve layers of the retina
includes four stages. At the first stage, outer segments of the rods and cones are lost.
At the second stage, apoptosis of the rods and cones is detected, which leads to a
violation of their interaction with the network of amacrine and bipolar cells. After
this, apoptosis of most neurons is induced. The remaining retinal cells search for
sources of stimulating signals, which leads to the migration of bipolar and amacrine
cells to the outer and inner border membranes. The retina, losing its layered struc-
ture, loses the capacity for phototransduction. At the last stage of the disease, meta-
bolic processes are disrupted, and neurons devoid of oxygen and nutrients enter
necrosis, being replaced by glial cells (Maksimova 2008; Marc et al. 2003). Thus,
the dystrophic processes of the retina are based on metabolic disorders of photore-
ceptor proteins, pigment epithelium and retinal neurons.
However, the vascular factor is also essential in the development of degeneration
of the retina of the eye. It is known that age-related changes in the arterial system of
the eye are always more distinct than in the venous system. With age, there is a
decrease in the number of functioning vessels, especially terminal arborizations and
anastomoses. The entire vascular tree with retinal ophthalmoscopy looks poor and
pale. The natural tortuosity of the arteries and veins disappears; they become
straightened. The lumen of the vessels narrows down evenly along the entire length;
the light reflex from the vascular walls is weak; and it dims as the calibre of the ves-
sel decreases. Fluorescein angiography data indicates a significant slowdown in
blood flow in both the arterial and venous systems of the retina in people over
65 years of age. The avascular zone of the macular region becomes wider; the char-
acteristic structure of the vascular arcade disappears. Morphological studies indi-
cate the development of fibrosis and hyaline degeneration of the vascular wall,
thickening of the basement membrane, and collagenisation of fibrils.
Involutional desquamation of the vascular endothelium, elastofibrosis, and thick-
ening of the wall as a result of fibre swelling and plasma infiltration of the intima
lead to the narrowing of the lumen of the vessel. At the same time, vessels cease to
4 1 Literature Review
be flexible, become dense, rigid and lose their adaptive capabilities, including dur-
ing variations in arterial and intraocular pressure as well. Anatomical and morpho-
logical degradative changes of the choroid and retina lead, respectively, to a
disruption in the functional activity of the latter. According to L. Justino et al.
(2001), with age, there is a significant decrease in bioelectric activity and an increase
in the duration of nerve impulses in the retina due to involutional changes (Justino
et al. 2001). According to the authors, a decrease in the intensity of transcapillary
metabolism in the vessels of the retina and choroid leads to the development of
senile hypoxia of the retina with a decrease in metabolic processes and, as a result,
a decrease in visual functions (Shamshinova and Volkov 1999; Justino et al. 2001).
All this causes the appearance of senile retinal haemorrhages, and also contributes
to the occurrence of dystrophic changes in the retina (Friedman et al. 1998).
According to Delori F., with age, the fundus autofluorescence spectrum shifts by
10–20 nm toward shorter wavelengths. According to the authors, this is due to an
increase in the number of fluorophores in Bruch’s membrane (Delori et al. 2001).
Involutional changes in the retina and choroid contribute to the appearance of senile
retinoschisis, annular (engirdling) retinopathy. The outcome of a retinoschisis can
be retinal detachment with all its consequences. The course of the pathological pro-
cess can be slow or, alternatively, very fast with the appearance of scotomas and a
decrease in visual acuity, if the process affects the macular region. But age-related
changes in the retina do not in all cases lead to the development of macular degen-
eration (Kornzweig 1965; Sarks 1976). However, a decrease in the adaptive capa-
bilities of the organism against the background of involutional changes creates
favorable conditions for the occurrence of pathological processes in the choroid and
retina (Bressler and Bressler 1995; Kornzweig 1965).
Disruption in blood patency in the arterial and venous vascular bed leads to isch-
emic changes in the retinal tissue with the development of secondary dystrophies.
The microcirculatory bed always reacts to the influence of a pathogenic factor as a
single integral system. Therefore, it is extremely difficult to determine the causal
link in changes observed.
1.1.1 Molecular Mechanisms of Age-Related
Macular Degeneration
The main reason for the loss of central vision in the elderly is age-related macular
degeneration, which is a chronic dystrophic process that affects mainly the retinal
pigment epithelium. Photoreceptors are also included in the pathological process as
a result of their close interaction with the retinal pigment epithelium, which leads to
a decrease in central visual acuity. The pathogenesis of age-related macular degen-
eration is based on processes such as retinal cell aging, dystrophic changes in the
intercellular matrix, impaired angiogenesis, and lipid metabolism (Shaw et al. 2016;
Stone 2007).